1.If updating from a ' release candidate' first completely un-install previous version.Then Go to > Windows search bar and type in %appdata% then in the Roaming data folder delete the entire QCAD file.Then install QCAD 3 final. The roaming data will just be re-built!

2. The library files should be readable - but try setting the permissions and see if this has any effect.Navigate to the QCAD installation folder and right click on it > then in the security tab set the permissions for yourself to read and write.